1. Field of the Invention
The invention relates generally to non-linear optical devices, and more particularly, to optical frequency-converters.
2. Discussion of the Related Art
Herein, optical frequency-conversion refers to a process that directly converts light of one frequency into light of another frequency without intermediate conversion of the light into electrical signals. Materials with large cross sections for certain nonlinear optical processes are able to produce optical frequency-conversion. Lithium niobate has large cross sections for such processes and thus, has been used to construct optical frequency-converters.
Unfortunately, lithium niobate also has properties that are not desirable in optical frequency-converters. In particular, standard lithium niobate has iron as an impurity. Due to the iron impurities, the intense illumination needed for frequency-conversion causes a photorefractive effect that can spatially modulate the refractive index of lithium niobate. The refractive index of lithium niobate will be spatially modulated during optical frequency-conversion unless special precautions are taken. Such uncontrolled spatial refractive index modulations would interfere with the quasi-phase matching required for optical frequency-conversion. To avoid the iron-induced refractive index modulations, special precautions are taken to maintain lithium niobate at a high temperature during optical frequency-conversion.
It is desirable to have optical frequency-converters that efficiently generate light without the need for special precautions during operation.